In the USA I tipped, after being told off by a bargirl, I mean a couple of dollars, who cares. I always found I got better service after tipping the first time.
In Oktoberfest in Munich, we paid $20 each for our first steins, so the beer maids would come back to us!
I used to shake my head at window washers too. But now I think, ah fuck it, give them a dollar. At least they aren't begging on a street corner & doing nothing for it. Why not help them out